Fusible powdered metal paste

ABSTRACT

There is provided an inorganic salt-free, anhydrous, noncorrosive powdered solder metal paste and vehicle therefor which vehicle is characterized by the presence therein of a flux and a nonaqueous organic liquid having a surface tension or surface energy of from 43 to 65 dynes/cm. and higher at 20°C. When powdered solder metal or powdered solder metal alloy is distributed in such a vehicle in an amount sufficient to form a paste, a deposit will not undergo hot slump at elevated temperatures. The pastes and vehicles are free of inorganic metal salts.

RELATED APPLICATION

This application is a continuation-in-part of my copending applicationSer. No. 546,794 filed Oct. 31, 1983 now abandoned.

This invention relates to a paste vehicle and a heat-fusible metalpowder. The vehicle is especially useful for making noncorrosivemetalliferous pastes for joining by soft soldering.

BACKGROUND OF THE INVENTION AND PRIOR ART

The joining or coating, using a fusible soft solder metalpowder-containing paste can be done efficiently, provided, however, thatupon heating and before fusion of the metal, the soft solder metalpowder containing paste exhibits controlled hot slump; in other words,the metal powder stays substantially where and as the paste wasdeposited on the substrate. This primary property has been difficult toobtain with conventional metal powder-containing pastes. The instantvehicles and pastes provide such property.

Restriction of flow of any resulting fused metal (that is a lack ofgeneral spreading), except into intended joints or to form intendedjoints as in the joining of electronic components to printed circuitboards or hybrid circuit board to avoid bridging in surface mounteddevice attachments, are other properties desired. The inventive productshere can also provide desired restriction of metal flow on remelting.For most electronic soldering purposes at this time, the compositionmust be free of corrosive agents such as inorganic salts.

Soft solder pastes, for example, (melting below 400° C., preferablybelow 330° C.) usually contain tin and lead; a little silver often isalloyed with the tin, particularly for electronic work, e.g., for makingmicroelectronic connections. Soft solder pastes now are experiencingwider acceptance in industry, primarily because pastes are more readilyadapted to automated manufacture and screen-printing on a substrate thanare the more conventional and manually effected solder bar, separateflux and iron, or solder wire (e.g., one containing the flux in a corewithin the wire) and an iron. The make-up of prior powdermetal-containing paste compositions has been largely influenced by theprior practices particularly in respect of fluxing or surface preparingagents. These have comprised substantial portions of organic acids,e.g., rosin acid, inorganic salt materials, e.g., zinc chloride,ammonium chloride, borax and the like, and rosin-based fluxes.

These soft solder compositions have not been entirely satisfactory in anumber of respects. First, because of the presence of inorganic saltfluxes they have tended to be corrosive to the base metal or tointroduce water as water of hydration leading to spattering. Thisproblem was alleviated to a great extent with rosin-based flux vehicles.However the rosin-based fluxes or vehicles permit excessive movement ofthe solder particles away from the deposition site on heating; they alsooften give rise to sputtering and "dewetting" which leaves a residue asa halo around the solder joint. Their solder pastes have been prone toexcessive solder balling, i.e., the formation of discrete minute ballsof soft solder. This is highly undesirable and leads to electricalbridging across what should be electrically isolated connectionsespecially on printed circuit boards.

In the preferred embodiment of a soft solder composition an alkalisolubilized in a polyhydric alcohol, e.g., glycerine, acts as a fluxingagent and improves solderability. For best results herein, in a softsolder metal powder, a slump control system and an inorganic salt-freefluxing system are present. The compositions hereof are practicallynoncorrosive and easy to formulate and handle. They are readilyadaptable to screen printing. Disadvantages attendant priorcompositions, such as spattering due to evolution of water vapor, solderballing and bridging, corrosivity, dewetting, tenacious residue, failureof the solder to melt due to excessive oxidation, etc., are not observedin the metal-bearing pastes here. "Inorganic metal salts" are metal orammonium salts of inorganic acids Lange's "Handbook of Chemistry", 10thEdition, pp. 209-333.

To better understand the applications of solder pastes, reference may behad to "Technology of Electronic Grade Solder Pastes" Taylor et al,Solid State Technology, September 1981, pages 127-135.

One prior paste composition is disclosed by Knoth U.S. Pat. No.1,772,952. This paste comprises a solder metal powder, an amine and abinder or vehicle such as vaseline. These compositions do not, however,possess antislump properties which are currently in demand in theelectronics industry. U.S. Pat. No. 2,493,372 to Williams dated Jan. 3,1950 discloses a paste composition including a metal powder, e.g.,tin-lead, a salt flux, and a C, H and O compound. Reference may also behad to U.S. Pat. No. 3,954,494 dated May 4, 1976 which discloses awax-flux composition. U.S. Pat. No. 804,664 also shows a tin-lead metalpowder paste in a vaseline--glycerine--inorganic salt flux system.

Another solder paste composition comprising powdered solder, a resin, asalt of an amino acid ester and a solvent is discussed by Melchiors etal in U.S. Pat. No. 3,065,538 dated Nov. 27, 1962.

Another aqueous base solder composition is shown by Johnson in U.S. Pat.No: 3,073,270 dated Jan. 15, 1963.

Also exemplary of prior solder paste compositions is the patent toPetersen et al U.S. Pat. No. 3,925,112 dated Dec. 9, 1975. Accordingthis invention, there are provided emulsified self-cleaning solderingfluxes having an aqueous phase including from 2 to 3 pbw (parts byweight) of a water soluble hydrazine salt and an oil phase includingfrom 5 to 50 parts of a mixture of petrolatum and wax. Also provided arewater solutions of 2 to 30 pbw of the water soluble hydrazine salt, upto 5 parts of a vegetable gum thickener, a wetting agent and the balancewater.

Another prior paste composition is disclosed by Mastrangelo in U.S. Pat.No. 4,273,593 dated June 16, 1981. This paste comprises a solder metalpowder and a vehicle, the latter being a hydroxypropyl cellulose blendedwith glycerine and/or water and further blended with a mixture ofpolyalkoxyalkanols.

It has now been found that an improved vehicle for the instant powderedmetal solder pastes is provided as an essentially inorganic salt freenonaqueous vehicle medium comprising a normally liquid nonaqueousorganic liquid as an antislump agent, usually and preferably apolyhydric alcohol system, characterized in that the liquid has aminimum surface tension of 43 dynes/cm (20° C.), and generally from 43to 65 or higher dynes/cm. Such system provides a slump control propertyto the metal bearing paste such that when it is heated toward themelting point of the soft solder metal powder, e.g., 118° C. to 325° C.,the shape of the deposit is substantially maintained until the metalfuses. Although as will be seen from Table I below, and nonaqueousliquid having a surface tension above 43 dynes/cm. may be used in thevehicles hereof, polyols are the most practical antislump materials andthe invention will be described with reference to polyols forconvenience.

These vehicles also desirably include a low surface energy material suchas a hydrocarbon. The hydrocarbon, which is preferably solid orsemi-solid (e.g., greaselike) melts, of course, and wets the substratearound the deposit, but carries no significant amount of the metalparticles with it. Although hydrocarbons having melting points above 15°C. are preferred, in certain embodiments normally liquid hydrocarbonssuch as hexane, cyclohexane, toluene or mixtures thereof, e.g., mineralspirits, may be used. The high surface energy material serves as abinder under heat conditions to hold the particles in position. Also thehydrocarbon is easily cleaned, along with any residue that may be left,away from the joint or surrounding area. The hydrocarbon by itself isincapable of imparting slump control properties to a powdered metalcontained therein. In the preferred powdered metal compositionsespecially adapted for screen printing, no dewetting is observed.Surprisingly, even after melting, the fusible metal resists running fromthe site of application. Of course, in soft solder compositions there isalso need for a fluxing agent. Such agent serves to clean the surfacesof the substrate or joining metal as well as the solder particles, andto inhibit the formation of oxide coating on the solder particles as thetemperature is elevated toward melting.

The desirable properties of antislump, anticorrosion and freedom fromspattering in the metal-bearing pastes here are not observed in priorcompositions known to me. Other additives may desirably be present aswill be pointed out below. The instant pastes have no water in themother than insignificant amounts possibly present as an adventitiousimpurity that might be associated with good quality technical gradeingredients. No water is added deliberately as such or as a hydrate; soit can be said that the instant pastes and vehicles are "non-aqueous" asa practical matter. Also, it has been found that the high surfacetension liquid, e.g., a polyol, can be a single component vehicle or apart of a multicomponent vehicle, i.e., including also a hydrocarbon.The substrate on which the paste is deposited has no significant effecton the hot slump resistance.

BRIEF STATEMENT OF THE INVENTION

Briefly stated, the present invention is a nonaqueous or anhydrousinorganic salt-free, powdered solder metal paste composition comprisinga major amount of a soft solder metal powder and a minor amount of apaste vehicle containing a noncorrosive anhydrous fluxing agent, and anantislump composition including a nonaqueous liquid having a surfacetension above 43 dynes/cm. at 20° C. and preferably a polyol containingfrom 2 to 6 hydroxyl groups and having a surface energy of from 43 to 65or higher dynes/cm. (20° C.). Preferably these pastes also include apaste forming vehicle ingredient which is a hydrocarbon.

To further extend the utility of the soft solder alloys, there may beadded other ingredients, such as, one or more surfactants, one or morecondensed or fused ring aliphatic acids, e.g., cholic acid or abieticacid or rosin acids, and one or more plasticizers such as di-n-butylphthalate. The pastes including a powdered soft solder alloy form ashiny and coherent (i.e. coalesced) solder pool in a controlled area ofapplication.

DETAILED DESCRIPTION OF THE INVENTION

It has been found that slumping of a paste composition containing amajor amount of a powdered soft solder metal or soft solder metal alloycan be effectively controlled by a unique composition composed of ahydrocarbon or a mixture of hydrocarbons, e.g., petrolatum, and apolyhydric material, e.g., glycerine and sodium hydroxide. Thecombination of a hydrocarbon having a melting point of at least 15° C.and less than the melting point of the metal, and a polyhydric alcohol,such as di- or triethanolamine, or glycerine, or pentaerythritol, or thelike, is however, effective in maintaining quite substantially theprofile of the paste as it was initially deposited on the surface orsubstrate. A solder paste requires, however, a flux. At the fusionpoint, the metal in the present compositions has not run or spattered orballed up into small discrete balls of molten metal prior to the fusionof the entire mass. A polyhydric alcohol or polyol alone also is capableof conferring this property upon a paste composition containing a majoramount of a metal or a metal alloy. However, the composition isunsatisfactory as a soft solder composition, requiring also a suitablehydrocarbon diluent and a noncorrosive flux.

To form a solder paste, the vehicle portion hereof are blended with apowdered solder alloy to the extent of from 75% to about 93% metal byweight of the paste, and desirably from 80% to 90%, and preferably about85% powdered metal. The particle size of the powdered metal is desirablysuch that it will not settle out of the vehicle which is quite viscous(20,000 to 200,000 cps., Brookfield No. 7 spindle at 20 rpm) onstanding. In general, the particle size is less than 100 mesh (U.S.Standard Sieve Size), desirably-200+400 mesh. A mixture of various sizesand/or shapes of metal powders often is advantageous for achievingdesired rheology and other paste properties in these applications.Solder powder particles are available in two forms, i.e., those havingirregular shape and those having spherical shape. Either shape, or amixture thereof maybe used, although the spherical shape is desired.Example 131 below is the best mode presently known to me of practicingmy invention. Where normally liquid hydrocarbon diluents are used, e.g.,toluene, the particle size of the solder powder should be less thanabout 10 microns in order to minimize settling.

Preparation of the vehicle and paste is achieved with conventionalstirring or blending means. Warming can be done, if necessary ordesired, to facilitate by dissolving or melting ingredients together forputting them into very intimately dispersed condition and/or otherwisemaking a multiphase dispersion with the ingredients in a very fine stateof subdivision preparatory to blending with the metalliferous powder toform a mass of paste consistency. Preferred compositions includeadditional fluxing agents, optionally a surfactant, optionally anorganic carboxylic acid, and optionally a diluent; i.e., a plasticizerand/or solvent. Each of these ingredients will be discussed below.Thereafter, the solder alloys will be discussed followed by generalprocessing techniques, and specific examples.

THE HYDROCARBON INGREDIENT

Hydrocarbons are preferred ingredients for the metal paste compositionsthereof. Fluorinated hydrocarbons or chlorofluorinated hydrocarbons maybe used to replace part or all of the hydrocarbon. The useful materialsrange in melting point from below about room temperature to normallysolid materials, e.g., petroleum hydrocarbon waxes containing from 18 to60 or more carbons and melting in the range of 28° C. to 100° C. Theuseful hydrocarbons also have a very low ash or solid residue contentand either melt and flow, sublime and/or thermally decompose at atemperature below the melting point of the solder (i.e., below 330° C.).The amount of ash or solid residue from the hydrocarbon remaining of themelt temperature should be less than 0.5% and preferably less than 0.1%.The useful hydrocarbons may be paraffinic, aromatic, or mixed aromaticparaffinic or mixtures of compounds of such characteristics, and includevarious mixtures of hydrocarbons, e.g., octadecane, mineral spirits,paraffin wax, and petrolatum, e.g., Vaseline. Synthetic hydrocarbonsnormally solid or semi-solid include commercially availablepolyethylenes, polypropylenes, poly(ethylene-propylene), polybutenes,poly(ethylenestyrene), hydrogenated nonpolar polymeric hydrocarbonshaving Ring and Ball softening points of from 15° C. to 130° C., suchpolymers having a molecular weight less than about 1500 and preferablyless than 1000, hydrogenated polyterpenes, etc. The best material knownto me for use herein is petrolatum. Halogen substituted hydrocarbonse.g., fluorocarbons and chlorofluoro carbons may also be used, they alsobeing relatively inert at the temperatures encountered.

"Petrolatum" is a well known colloidal system of nonstraight-chain solidparaffinic hydrocarbons and high boiling liquid paraffinic hydrocarbons,in which most of the liquid hydrocarbons are held inside the micilles. Adetailed historical account including the chemistry of petrolatum andmodern manufacturing methods is found in Drug and Cosmetic Industry,Vol. 89, 36-37, 76, 78-80, and 82, July 1961. "Petrolatum for Drugs andCosmetics" Schindler. Petrolatum is typically a yellowish to amber orwhite semisolid, unctuous mass, practically odorless and tasteless. Ithas a density at 25° C. of from 0.820 to 0.865, a melting point of 38°to 54° C., and a refractive index η60.0 of 1.460-1.474. It is readilycommercially available under the well known proprietary marks Vaseline,Cosmoline, Stanolene, Penreco brand petroleum jelly as well as otherconvenient trade designations. Petrolatum may be used in itscommercially available form or it may be modified by the addition ofpetroleum wax or paraffin wax in particulate form, e.g.,microcrystalline wax.

The hydrocarbon ingredient is utilized in an amount which ranges from 10to 90 pbw of the vehicle system, or 0.7% to 22.5% of the solder paste. Anonaqueous organic liquid having a surface energy in the range of 43 to65 or higher dynes/cm appears to be essential for the slump controlcharacteristics of the present powdered metal pastes. Although water hasa high surface energy as does sulfuric acid, these materials are notsatisfactory because of spattering or reactivity at elevatedtemperatures.

SLUMP CONTROL SYSTEM

As indicated above, the ability of a soft solder paste to resist hotslump, or running during softening and melting is essential in modernmicroelectronic processing and particularly silk and stencil screeningof soft solder pastes. It has been found that a combination of ahydrocarbon as above defined and particularly petrolatum, and anonaqueous organic liquid having a surface tension at 20° C. greaterthan 43 dynes/cm., and preferably one or more polyhydric alcoholscontaining 2 to 6 OH groups and having a surface tension or energy offrom 43 to 65 or higher dynes/cm at 20° C., is effective in providing agood paste and in preventing slumping of the metal particles. Thehydrocarbon alone with powdered soft solder composition appearsincapable of conferring this property to any degree. Nonaqueous organicliquid alone gives sufficient antislump properties but sometimesinsufficient soldering properties. Soft solder pastes also require aflux and to obtain the non-corrosiveness required in modern electronicapplications the flux should not be an inorganic salt, e.g., ZnCl₂, NH₄Cl, or borax, this latter being highly hydrated and thus given tospattering.

The antislump agents hereof are generally polar compounds.

Table I below gives specific examples of liquids of various kinds usefulin inhibiting slump. The polyols useful herein are aliphatic andnormally liquid or of relatively low melting point, i.e., below about170° C. and include ethylene glycol, diethylene glycol, propyleneglycol, dipropylene glycol, sorbitol, mannitol, trimethylolethane,trimethylolpropane, diethanolamine, triethanolamine, pentaerythritol,and erythritol. These polyols coact with a hydrocarbon, especiallypetrolatum in the absence of water and in the presence of a finelydivided metal powder to control slumping on heating and to provide asatisfactory paste medium. A fluxing agent either as a separateingredient, e.g., sodium hydroxide, or as a moiety of the polyol (e.g.,triethanolamine or diethanolamine) must be present. The secondary ortertiary amine group appears to be suitable for fluxing. The polyol isgenerally insoluble in the hydrocarbon. The amount of liquid polyolconstitutes from about 0.5% to 10.0% by weight of the vehicle andpowdered solder metal composition.

A comparative study of various agents in 88.9% powdered metalcompositions demonstrates the significance of the limitation respectingsurface energy or surface tension.

                  TABLE I                                                         ______________________________________                                        Slump/Resistance Study                                                        (For 60% Sn; 40% Pb Powdered Metal)*                                          Surface                Slump                                                  Tension Antislump      Resis-                                                 (Dyne/Cm)                                                                             Agent          tance   Remarks                                        ______________________________________                                        63.4    7% NaOH/93%    Yes     Fluxing occurred                                       Glycerine                                                             63.4    Glycerine      Yes     No fluxing                                     58.2    Formamide      Yes     Little fluxing                                                                occurred                                       55.1    Conc H.sub.2 SO.sub.4                                                                        Yes     Oxidizing occurred                             50.8    Methylene Iodide                                                                             Yes     P/M turned green                               48.4    Triethanolamine                                                                              Yes     Fluxing occurred                               48.5    Diethanolamine Yes     Fluxing occurred                               48.3    Monoethanolamine                                                                             Yes                                                    47.7    Ethylene Glycol                                                                              Yes     Little fluxing                                                                occurred                                       45.2    Triethylene Glycol                                                                           Yes     Little fluxing                                                                occurred                                       44.0    Tetraethylene Glycol                                                                         Yes     Little fluxing                                                                occurred                                       44.5    Polyethylene Glycol                                                                          Yes     Little fluxing                                         200                    occurred                                       44.5    Polyethylene Glycol                                                                          Yes     Little fluxing                                         600                    occurred                                       42.9    Aniline        No                                                     40.9    Phenol         No      Solid Chemical                                 38.0    Pyridine       No                                                     36.8    Nitromethane   No                                                     32.7    Acetic anhydride                                                                             No      Oxidizing occurred                             32.5    Oleic acid     No                                                     32.3    Carbon Disulfide                                                                             No                                                     27.8    Acetic acid    No      Oxidizing occurred                             27.5    n-Octyl alcohol                                                                              No                                                     25.5    Cyclohexane    No                                                     24.2    Ethyl bromide  No                                                     23.0    i-Butyl alcohol                                                                              No                                                     20.7    t-Butyl alcohol                                                                              No                                                     --      Vaseline       No                                                     ______________________________________                                         *NOTE:-                                                                       1. Formula used for slump resistance studies: 88.9%(97.5% Pb; 1.0% Sn;        1.5% Ag) + 7.8% Vaseline + 3.3% Antislump agent.                              Paste was examined on Cu coupon at designated temperature.               

Table II below shows the hot slump effect on a solder composition usingthe "antislump agent" as the sole vehicle.

                  TABLE II                                                        ______________________________________                                        Slump/Resistance Study                                                        (60% Sn; 40% Pb/Single Phase Vehicle System)                                  Surface Tension                                                                         Antislump    Slump                                                  (Dyne/Cm) Agent        Resistance Remarks                                     ______________________________________                                        63.4      7% NaOH/93%  Yes        Excellent                                             Glycerine               Soldering                                   63.4      Glycerine    Yes        Oxidizing                                   55.1      Conc H.sub.2 SO.sub.4                                                                      Yes        Occurred                                    50.8      CH.sub.2 I.sub.2                                                                           Yes        Solid                                       48.9      Triethanolamine                                                                            Yes        Chemical                                    47.7      Ethylene Glycol                                                                            Yes                                                    40.9      Phenol       No                                                     38.0      Pyridine     --         P/M ppt'd                                                                     quickly                                     27.5      n-Octyl alcohol                                                                            --         P/M ppt'd                                                                     quickly                                     --        Vaseline     No                                                     ______________________________________                                         Note:-                                                                        1. Paste was examined on Cu coupon at 235° C.                          2. The vehicle NaOH/glycerine also provided good slump resistance for         Nordox Red Cuprous. (Cu.sub.2 O).                                        

Table III below shows the effect of temperature on hot slump resistancewith selected polyols and other additives.

                  TABLE III                                                       ______________________________________                                        Slump/Resistance Study                                                        (Temp. Effect)                                                                Surface Tension                                                                         Antislump     Temp. (°C.)                                                                       Slump                                      (Dyne/Cm) Agent         at Test    Resistance                                 ______________________________________                                        48.9      Triethanolamine                                                                             150        Yes                                                                235        Yes                                                                325        Yes                                        44.5      Polyethylene  150        Yes                                                  Glycol 200    235        Yes                                                                325        Yes                                        42.9      Aniline       150        No                                                                 235        No                                                                 325        No                                         38.0      Pyridine      150        No                                                                 235        No                                                                 325        No                                         ______________________________________                                         Note:-                                                                        1. Formula used for slump resistance studies: 88.9%(97.5% Pb; 1.0% Sn;        1.5% Ag) + 7.8% Vaseline + 3.3% Antislump agent.                              Paste was examined on Cu coupon at designated temperature.                    2. When the paste was examined on substrate which has been surface treate     with FC723* (surface tension 11 dyne/cm), the slump resistance behavior       was still about the same as that on the Cu coupon.                            *Fluorad FC723 is an oleophilic, hydrophilic fluorocarbon in an inert         vehicle having a specific gravity of 1.78 produced by 3M.                

FLUXING SYSTEM

As indicated above, there must be present a noncorrosive anhydrousfluxing system in a solder paste composition hereof. The fluxing systemmay be a single chemical specie dissolved or dispersed in thehydrocarbon/polyol system. Alternatively, the fluxing system maycomprise a plurality of fluxing agents dissolved or dispersed in thehydrocarbon/polyol system. Best results have been secured with alkali orbasic reacting fluxing agents, and particularly alkali metal hydroxides.These can be used as solutions in the polyol or as alcoholates of amonohydric or polyhydric alcohol, e.g., methyl, ethyl or isopropylalcohol, dissolved in the polyol, or the alkali metal salt of thepolyol, e.g., sodium glycerate.

The alkali metal hydroxide in such component is a preferred noncorrosivefluxing agent and is effective in a proportion of about 0.1-5% by weightof the vehicle, and, advantageously, 0.25-3.5%. The liquid polyol canconstitute from about 0.5 to 75.0% by weight of the vehicle, and,advantageously, about 40%. On the basis of the entire solder paste, theamount of polyol ranges from about 0.3 to 18.8%. The alkali metalhydroxides useful herein include in descending order of preferencesodium hydroxide, potassium hydroxide, lithium hydroxide and cesiumhydroxide. Such alkali metal hydroxides have a limited solubility inpolyhydric alcohols or mixtures of same that are liquid and areconveniently used in concentrations at or near the limit of solubility,i.e., less than about 10% by weight of the polyol. As indicated, theycan be present as an alkali metal alcoholate, e.g., sodium ethylate,dissolved or well dispersed in the polyol, the alcoholate beingequivalent to the hydroxide. The polyhydric alcohols include glycerine(which is preferred), ethylene glycol, diethylene glycol, propyleneglycol, sorbitol, mannitol, pentaerythritol, erythritol, etc.,containing from 2 to 6 OH groups. A sodium hydroxide/glycerine solutionis particularly effective and may be used as the sole fluxing agent, orit may be used in combination with an alkanolamine, e.g.,triethanolamine or diethanolamine to provide effective fluxing systemsfor the instant pastes.

A useful fluxing ingredient is also provided as an amine component ofthe vehicle. Such component is effective in a broad proportion, e.g.,about 2-40% by weight of the vehicle and, advantageously 3-10%. Theessential functional group of this component is an ##STR1## wherein R,R₁, and R₂ are independently selected from hydrogen, alkyl, alkylene,cycloalkyl, cycloalkylene, carboxyalkylene, aminoalkylene,hydroxyalkylene, carboxyalkyl, etc., no more than two of R, R₁ and R₂being hydrogen. The alkyl and cycloalkyl groups may contain from 1 to 30carbon atoms. The amine component may contain one to three amino groups.A particularly useful group of amine compounds is the water solublealkanolamine group including mono-, di, and trimethanolamines, mono-,di-, and triethanolamines; mono-, di-, and tripropanolamines, andmixtures of the mono-, di-, and trialkanolamines. Alkyl and cycloalkylamines, particularly the C₂ -C₁₈ mono and polyamines, e.g.,triethylamine, tri-isopropylene, diethylamine, mono-n-butyl amine,propylene diamine cyclohexylamine, cyclopropyl methylamine,tetramethylene diamine, rosin amine, cyclohexylamine hydrochloride,cyclohexylene amine, diaminoethylamine, diaminopropylamine, etc. Thus,the kind and configuration of the amino compounds useful herein are verybroad and results among the examples are reasonably equivalent forfluxing. Amidino and guanidino fluxing agents, advantageously aliphaticones, can be considered as useful amines for the instant purpose.Aromatic amines, while functional, often impart toxicity and thereforeare not favored. Similarly, pyridine-type materials, such as, pyridineor a lutedine give off intensely objectionable odors and are notfavored, but could be considered functioning like amines here. Thepreferred amines are the alkanolamines. Also useful to supplement thebase system are the amino acids, particularly the water solubleamino-acids, e.g., aminoacetic acid, beta-aminopropionic acid,(beta-alanine)aminobutyric acids, epsilon-aminocaproic acid, N-methylglycine, betaine, alpha-delta-diaminovaleric aliphatic carboxylic acids.Thus, urea, propionamide, butanamide, 2,2-dimethylpropionamide,N-methylpropionamide, N,N-beta-trimethylbutyramide, steroylamide, etc.,can be such base system supplements.

OTHER FLUXING AND/OR SOLDERABILITY INGREDIENTS

Organic carboxylic acids are useful as fluxing and/or solderabilityingredients, particularly in a supplemental role in combination with theother ingredients described above. Any high boiling (above 300° C.)aliphatic carboxylic acid may be used. I prefer, however, to usecondensed ring acids such as abietic acid, cholic acid, rosin acids,polymerized rosin acids, hydrogenated rosin acids rosin estersdisproportionated rosin ester gum, wood rosin, gum rosin, tall oilrosin, or fatty acids such as stearic acid, oleic acid, etc. Fatty amineand fatty acid compounds are also useful in this capacity. Examplesinclude N-tallow-1,3-diaminopropane, 3-diaminopropane dioleate, etc. Theacids are used in small amounts of from 0.5 to 10% by weight of thevehicle composition, or on the basis of the fully formulated solderpaste, from about 0.03% to about 2.5%.

It has also been found that a surfactant may be advantageously includedin the vehicles hereof. Although such surfactant or wetting agent may beanionic, cationic, amphoteric, or nonionic, nonionic agents arepreferred. Many surfactant materials are known. They are used in thepresent vehicles to help to control the rheological properties,shelf-life stability, air voids, etc. The amount used is determined bycut and try and is that amount which is sufficient to impart the desiredcontrol. These agents assist in the dispersion of the powdered metal andin carrying the fluxing agent to the surfaces being joined or coated.Generally less than 10% by weight each of other ingredients is used andusually from 0.01% to 5% by weight of the vehicle or 0.001% to about4.5% of the solder paste.

Specific surfactants include the alkylarylpolyether alcohols, ammoniumperfluorinated carboxylates, fluorinated alkyl esters of fatty acids,acetylenic glycols (which as sometimes can act as a defoamer),polyoxyethylene sorbitan monostearate, etc. Surfactants commonly used insolder monostearate, etc. Surfactants commonly used in solder pastes maybe used herein.

Solvents and/or diluents may also be present in the vehicle compositionshereof. For example, when a paste containing powdered solder metal is tobe used in a screen printing process, solvents are conveniently used toadjust the viscosity to a satisfactory level. Solvent materials aredesirably volatile, at least at the melting point of the solder alloy.Any solvent including low molecular weight alcohols, e.g., ethyl orpropyl, isopropyl, butyl, amyl, cyclohexyl, terpene alcohols, etc.;ketones; e.g., methyl ethyl ketone, methyl isobutyl ketone;2-butoxyethanol-1, ethylene glycol dimethyl sulfoxide, hydrocarbons,e.g., kerosene, terpene hydrocarbons, hexane, cyclohexane, heptane,octane, naphthas such as mineral spirits, ethyl acetate, amyl acetate,etc. The solvent ingredients may also include higher boiling materialscommonly regarded as plasticizers such as dibutyl phthalate, tricresylphosphate, etc.

The selection of the solvent and/or diluent is controlled by the enduse, cost, environmental factors, desired plasticity, etc. The solventor diluent may be water soluble or substantially water insoluble. Thesolvent or diluent leaves the system after application to a substrate asin screen printing, the residue being the solder paste compositionhereof.

Minor amounts of known odorants, bactericides, fungicides, etc., mayalso be included in the vehicles hereof if desired. Amounts of suchingredients usually range from about 0.1 to 2% by weight of the vehicle.

PREPARATION OF THE VEHICLES

The simplest preparation of the vehicles hereof involves only effectivemechanical mixing of the ingredients into the petroleum hydrocarboningredient, e.g., petrolatum.

The hydrocarbon can, if desired or necessary, be heated to melt it andfacilitate the blending operation, and warming of some of the otheringredients also can be of help. If it not necessary that the mixture bea solution. The paste-like vehicle can be cloudy and contain one or morephases with the disperse phase fine enough so that it will not separatesubstantially on standing.

The materials discussed in detail above are considered to be ingredientsof the vehicles hereof.

THE METAL POWDER

Solder compositions useful herein as the metal powder for blending withthe above described vehicles to form a paste, or for extrusion of ahollow wire for making a cored solder wire, are well known. A number ofrepresentative compositions useful herein are given in the Taylor et alarticle, supra. In general the solder compositions have a melting pointin the range of from about 118° C. to about 330° C. and comprise tintogether with lead and/or silver. Other metals such as zinc, aluminum,bismuth, cadmium, nickel, indium and cadmium may also be used in thesolder compositions.

For making a solder paste, the metal powder is comminuted so that it iseasily and stably dispersed in the vehicle by grinding, ball milling,paddle blending, ribbon blender, etc. The entire powder should passthrough a 50 mesh screen (U.S. Sieve Series) (297 microns). Typically,the powder is finer than 100 mesh (149 microns) because larger particlesare difficult to disperse and maintain in suspension in the paste. Aparticle size in the range of -200+400 mesh (U.S. Sieve Series) ispreferred. Even smaller particle sizes, i.e., 10 microns or less aredesired where normally liquid hydrocarbons are used in the vehicle as insilk screening paste compositions. For most purposes, from 3 to 20 partsby weight of solder metal powder is blended with 1 part by weight ofvehicle. The paste compositions hereof generally will have a viscosityin the range of 20,000 cps to 200,000 cps. The preferred apparentviscosity will depend on the method of dispensing or application of thesolder paste to the materials to be joined. Hand trowelling pastes aremore satisfactory at the higher apparent viscosities than pastesintended for automatic dispensing such as extruding, flowing or sprayingonto a substrate or those which are most suited for application to asubstrate, e.g., a printed circuit, by a screen printed process.Viscosity can be controlled easily by the amount of solvent or solventmixture and/or plasticizer employed in the vehicle, or by the vehicle topowder ratio. Pastes often are degassed at reduced pressure.

In fabricating cored solder wire, conventional procedures are usedsubstituting a vehicle of the present invention for a conventional corecomposition such as a rosin based paste.

Effective control of hot slump in solder pastes is demonstrated by thefollowing specific examples. These examples are intended to enable thoseskilled in the art to apply the principles of this invention inpractical embodiments, but are not intended to limit the scope of theinvention. In this specification all temperatures are in degrees Celsiusunless otherwise stated, all parts, percentages, and ratios are byweight unless otherwise expressly stated, and sieve sizes are for theU.S. Standard Sieve series.

Testing for resistance to hot slump of a solder paste was done byapplying a deposit of the paste (about 5 mm diameter by 4-5 mm high) byspatula to a copper coupon, then gradually and automatically warming thecoupon with a Browne Corporation reflow instrument (in effect anautomated travellng hot plate) from room temperature to 330° in about ahalf-minute to a minute. The thus-heated deposit was observed visuallyfor collapse of the metal prior to its fusing as the vehicle disappearedtherefrom. Significant collapse of particulate metal of the depositprior to its fusion would indicate hot slump. None of the exemplarypastes given below showed significant hot slump. In the case of solderpaste the spreading of molten metal from the deposit area was alsoobserved in the same test. None of the exemplary tin-containing solderpastes given below showed significant spreading over the coupon; all haddesirably restricted flow. Great spreading away from the locus ofapplication is undesirable for many applications such as soldering inthe manufacture of electronic devices.

In the examples the petrolatum indicated as Petrolatum A was Vaselinebrand petroleum jelly, Vaseline being the trademark of ChesebroughManufacturing Co., Inc. for USP petrolatum sold at retail for householduse. The other petrolatums used were Penreco USP petrolatums, Penrecobeing the trademark of Pennzoil Co.; Petrolatum B was their Regent gradewhite petrolatum (Melting Point 118°-130° F.); Petrolatum C was theirRoyal grade (Melting pont 118°-130° F.); and Petrolatum D was theirAmber grade (Melting Point 122°-135° F.).

In the following examples the following designations have the followingidentities:

    ______________________________________                                        Triton* N-60 =                                                                             alpha-(nonylphlenyl)-omega-hydroxy-                                           poly(oxy-1,2-ethanediyl), (Regis-                                             try No.: 9016-45-9).                                             ______________________________________                                         *The trademark of Rohm & Haas Company                                    

    Armeen* HT = bis(hydrogenated tallow alkyl)amine,                             Armeen* RC = bis(C.sub.14 -C.sub.16 hydrocarbon alkyl)amine,                  Duomeen* T = N--tallow trimethylene diamine, and                              Duomeen* TDO =                                                                             N--tallow trimethylene diamino                                                dioleate, respectively.                                          ______________________________________                                         *The trademarks of Akzona, Inc.                                          

    PEG* 6000 DS =                                                                             alpha-(1-oxooctadecyl)-omega-[(1-oxo-                                         octadecyl)oxy]poly(oxy-1,2-ethanediyl),                                       (Reg. No.: 9005-08-07),                                          PEG* 6000 =  alpha-hydro-omega-hydroxy-poly(oxy-1,2-                                       ethanediyl), Reg. No.: 25322-68-3,                               Carbowax* 3350 =                                                                           a polyoxyethylenic wax,                                          n-Hexyl Carbitol* =                                                                        diethylene glycol mono n-hexyl ether, and                        Butyl Carbitol* =                                                                          diethylene glycol monobutyl ether,                                            respectively.                                                    ______________________________________                                         *The trademarks of Union Carbide Corp.                                   

    Fluorad* =   a liquid fluorocarbon.                                           FC-340                                                                        ______________________________________                                         *The trademark of 3M Company                                                 Surfynol* =  5-decyne-4,7-diol,2,4,7,9-tetramethyl,                           104E         Reg. No.: 126-86-3.                                              ______________________________________                                         *The trademark of Air Products and Chemicals, Inc.                       

    Dowanol* DM =                                                                              2-(2-methoxyethoxy)ethanol,                                                   (Reg. No. 111-77-3), and                                         Dowanol* DE =                                                                              2-(2-ethoxyethoxy)ethanol, (Reg. No.                                          111-90-0), respectively.                                         ______________________________________                                         *The trademarks of Dow Chemical Company                                  

Pastes tabulated below were made by blending the noncorrosive fluxingingredients, metal powder and other solderability ingredients withpetroleum hydrocarbon in a molten condition, then blending in the othervehicle ingredients when the mass cooled to 32°. The specification forthe solder powders was 5% max.+200 mesh, 4% max. -325 mesh. Theformulations were evaluated according to standards established forelectronic grade solder pastes. Accordingly, although some of theexemplified pastes may not have met all the electronic grade criteria,they were operative for other utilizing such as for making a joint usinga trowel to apply the paste. Of the exemplified solder pastes, thosepreferred for microelectronics work showed no solder balling.

In the solder tests no spattering was observed during heating to effectmelting, and no significant hot slump or solder spreading was observedthat is, they had good restriction of flow. Furthermore, there was nodewetting in evidence on the copper substrate, and cleaning of a jointeasily could be had with a suitable organic solvent, e.g., a petroleumnaphtha, alcohol, etc.

By way of contrast 20 parts of a prior art fluxing composition(specifically that of Example 1 of U.S. Pat. No. 3,925,112, which patentdiscloses some petrolatum as one of the ingredients in the oily phase ofan aqueous soldering flux emulsion) was compounded with 80 parts ofsolder alloy powder herein exemplified in the same manner as the pastesherein exemplified; resistance to hot slump was not demonstrated nor wasrestricted flow (spreading) of melted solder, and there was considerablespattering.

    ______________________________________                                        Alloy Powder: 97.5 Pb/1 Sn/1.5 Ag                                             Example No. 1      2      3    4    5    6    7                               ______________________________________                                        % Metal     80.0   85.0   85.0 85.0 85.0 93.0 93.0                            Components                                                                    Petrolatum A                                                                              12.3   10.5   10.5 10.5 10.5 5.0  5.0                             Triethanolamine                                                                           6.2    3.7    3.7  3.7  3.7  2.0                                  7% parts NaOH                                                                             1.4                                                               dissolved in 93 parts                                                         Glycerine                                                                     Triton N-60 0.1                                                               Armeen HT                      0.8            2.0                             Armeen RC          0.8                                                        Duomeen T                 0.8                                                 Duomeen TDC                         0.8                                       ______________________________________                                        Example No. 8      9      10   11   12   13   14                              ______________________________________                                        % Metal     85.0   85.0   90.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              8.0    10.0   5.6                 12.0                            Triethanolamine                                                                           1.9    1.0    3.3  5.0  5.0  5.0  2.7                             Glycerine   0.4    0.2    0.5  0.8  0.8  0.8                                  Cholic Acid 1.4    1.5    0.6  0.9  0.9  0.9  0.3                             PEG 6000    1.9    0.8                                                        n-Hexyl Carbitol                                                                          1.4    1.5                                                        Petrolatum B                   8.3                                            Petrolatum C                        8.3                                       Petrolatum D                             8.3                                  ______________________________________                                        Example No. 15     16     17   18   19   20   21                              ______________________________________                                        % Metal     93.0   93.0   93.0 93.0 93.0 93.0 93.0                            Components                                                                    Petrolatum A                                                                              3.9    5.0    5.0  5.0  3.9  3.9  3.9                             Triethanolamine                                                                           1.6    1.0              1.6  1.6  2.3                             7 parts NaOH                        1.5       0.8                             dissolved in 93 parts                                                         Glycerine                                                                     Armeen HT   1.5    1.0                                                        Ascorbic Acid             2.0                                                 Stearic Acid                   2.0       1.5                                  ______________________________________                                        Example No. 22     23     24   25   26   27   28                              ______________________________________                                        % Metal     93.0   85.0   85.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              3.9    8.3    8.3                 8.3                             Triethanolamine                                                                           2.3    5.0    5.0  5.0  5.0  5.0  3.3                             7 parts NaOH       1.7                                                        dissolved in 93 parts                                                         Glycerine                                                                     Stearic Acid                                                                              0.8                                                               Glycerine                 1.1  0.8  0.8  0.8  1.7                             Cholic Acid               0.6  0.9  0.9  0.9  1.7                             Pine Oil                                                                      Petrolatum B                   8.3                                            Petrolatum C                        8.3                                       Petrolatum D                             8.3                                  ______________________________________                                        Example No. 29     30     31   32   33   34   35                              ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 90.0 90.0                            Components                                                                    Petrolatum A                                                                              8.3    8.6    11.3 11.0 10.5 5.0  5.0                             Triethanolamine                                                                           5.7    3.3    3.4  3.7  4.2  3.8  3.8                             Glycerine   0.5                                                               Cholic Acid 0.5    1.5    0.3  0.3  0.3  0.2  0.2                             Pine Oil           1.6                                                        Butyl Carbitol                                1.0                             Di-n-butyl Phthalate                     1.0                                  ______________________________________                                        Alloy Powder: 10 Sn/88 Pb/2 Ag                                                Example No. 36     37     38   39   40   41   42                              ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              6.8    7.4    6.8  7.4  6.8  6.7  7.0                             Triethanolamine                                                                           6.0    6.4    6.0  6.4  5.2  6.6  6.4                             Cholic Acid 1.1    1.2    1.5       2.2  0.9  0.4                             Glycerine   1.03          0.7  1.2  0.8  0.8  0.6                             NaOH        0.07                                                              ______________________________________                                        Example No. 43     44     45   46   47   48   49                              ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 88.0 88.0 90.0                            Components                                                                    Petrolatum A                                                                              11.2   11.2   7.0  12.0 9.0  9.6  7.5                             Triethanolamine                                                                           2.3    3.4    6.5  2.7  2.8  2.2  2.3                             Cholic Acid        0.4    0.3  0.3  0.2  0.2  0.2                             Glycerine   1.2           1.2                                                 NaOH        0.3                                                               ______________________________________                                        Example No. 50     51     52   53   54   55   56                              ______________________________________                                        % Metal     94.0   85.0   90.0 90.0 90.0 90.0 90.0                            Components                                                                    Petrolatum A                                                                              4.5    12.0   7.2  7.0  7.1  6.8  6.8                             Triethanolamine                                                                           1.4    2.7    2.6  2.0  2.3  2.0  2.5                             Cholic Acid 0.1    0.3    0.2  0.2  0.2  0.2  0.2                             Surfynol 104E                  0.8  0.4  1.0  0.5                             ______________________________________                                        Example No. 57     58     59   60   61   62   63                              ______________________________________                                        % Metal     90.0   90.0   85.0 85.0 85.0 85.0 90.0                            Components                                                                    Petrolatum A                                                                              6.5    6.2    13.5 10.5 9.0  8.3  6.4                             Triethanolamine                                                                           2.5    2.8    1.2  4.2  4.5  5.2  2.4                             Cholic Acid 0.2    0.2    0.3  0.3  0.3  0.3  0.2                             Surfynol 104E                                 0.1                             Di-n-butyl Phthalate                                                                      0.8    0.8              1.2  1.2  0.9                             ______________________________________                                        Alloy Powder: 62 Sn/36 Pb/2 Ag                                                Example No. 64     65     66   67   68   69   70                              ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              8.3    8.3                                                        Triethanolamine                                                                           5.0    5.0    6.8  6.7  5.2  5.2  6.0                             7 parts NaOH                                                                              1.7                                                               dissolved in 93 parts                                                         Glycerine                                                                     Cholic Acid        1.7    1.5  0.8  0.8  1.5  1.1                             Glycerine                 1.5  0.7  0.7  1.5  1.1                             Petrolatum C              5.2  6.8  8.3  6.8  6.8                             ______________________________________                                        Example No. 71     72      73   74    75   76                                 ______________________________________                                        % Metal     85.0   85.0    85.0 85.0  85.0 85.0                               Components                                                                    Petrolatum A                    9.0   6.0  12.0                               Triethanolamine                                                                           3.7    1.5     6.8  6.0   9.0  2.7                                Cholic Acid 2.3    3.0                                                        Glycerine   2.2    3.0                                                        Petrolatum C                                                                              6.8    7.5     8.2                                                ______________________________________                                        Example No. 77     78     79   80    81  82   83                              ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              7.5    9.0    7.5  8.2  4.5  6.0  7.5                             Triethanolamine                                                                           7.2    5.2    7.5  5.4  5.3  4.5  3.8                             7 parts NaOH                        5.2  4.5  3.7                             dissolved in 93 parts                                                         Glycerine                                                                     Cholic Acid 0.3                                                               Glycerine          0.8         1.4                                            ______________________________________                                        Example No. 84     85     86   87   88   89   90                              ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              7.5    4.5    8.5  9.5  11.0 13.0 8.5                             Triethanolamine                                                                           3.8    3.8    2.5  1.3  1.3  1.0  4.6                             7 parts NaOH                                                                              3.7    3.7    2.5  1.2  1.2  1.0  1.6                             dissolved in 93 parts                                                         Glycerine                                                                     Cholic Acid                                   0.3                             Beta-Alanine       3.0    1.5  3.0  1.5                                       ______________________________________                                        Example No. 91     92     93   94   95   96   97                              ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              12.3   12.3   12.3 12.3 12.3 12.1 11.8                            Triethanolamine                                                                           1.1    0.9    0.9  0.9  1.1  1.1  1.1                             7 parts NaOH                                                                              1.1    0.9    0.9  0.9  1.1  1.1  1.1                             dissolved in 93 parts                                                         Glycerine                                                                     Butylcarbitol                                                                             0.5    0.9              0.5  0.7                                  Dowanol DM                0.9                                                 Dowanol DE                     0.9                                            Terpineol                                     1.0                             ______________________________________                                        Example No. 98     99      100  101   102  103                                ______________________________________                                        % Metal     90.0   85.0    85.0 85.0  85.0 85.0                               Components                                                                    Petrolatum A                                                                              7.8    10.6    10.6 11.7  11.6 11.5                               Triethanolamine                                                                           1.6    1.5     1.5  0.5   0.5  0.5                                7 parts NaOH                                                                              0.6    1.4     1.5  0.5   0.5  0.5                                dissolved in 93 parts                                                         Glycerine                                                                     Butylcarbitol      1.3     1.2  1.0   1.0  1.0                                Carbowax 3350      0.2     0.2  0.3   0.4  0.5                                ______________________________________                                        Alloy Powder: 96.5 Sn/3.5 Ag                                                  Example No.  104    105        106  107                                       ______________________________________                                        % Metal      80.0   80.0       80.0 80.0                                      Components                                                                    Petrolatum A 16.0   16.4       16.4 15.3                                      Triethanolamine                                                                             3.6    3.6        3.6 3.5                                       Cholic Acid   0.4                   0.4                                       Butyl Carbitol                      0.7                                       10% Florad FC 14 in                 0.1                                       Butyl Carbitol                                                                ______________________________________                                        Alloy Powder: 63 Sn/37 Pb                                                     Example No. 108    109    110  111  112  113  114                             ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              8.3    8.3    8.3  8.3  8.3  8.3  8.3                             Triethanolamine                                                                           5.0    5.0    3.3  6.7  1.7  5.7  1.7                             7 parts NaOH                                                                              1.7                                                               dissolved in 93 parts                                                         Glycerine                                                                     Glycerine                           5.0  1.0  1.3                             Cholic Acid        1.7    3.4                 1.2                             PEG 6000                                      2.5                             ______________________________________                                        Example No. 115    116    117  118  119  120  121                             ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 85.0 85.0                            Components                                                                    Petrolatum A                                                                              10.0   6.8    4.5  6.0  7.5  6.0  4.5                             Triethanolamine                                                                           1.0    6.0    5.3  4.5  3.8  3.8  3.8                             7 parts NaOH              5.2  4.5  3.7  3.7  3.7                             dissolved in 93 parts                                                         Glycerine                                                                     Glycerine   1.5    1.1                                                        Cholic Acid 1.5    1.1                                                        PEG 6000    1.0                                                               Beta Alanine                             1.5  3.0                             ______________________________________                                        Example No. 122    123    124  125  126  127  128                             ______________________________________                                        % Metal     85.0   85.0   85.0 85.0 85.0 90.0 90.0                            Components                                                                    Petrolatum A                                                                              8.5    9.5    11.0 13.0 11.8 6.2  6.5                             Triethanolamine                                                                           2.5    1.3    1.3  1.0  1.1  1.4  2.5                             7 parts NaOH                                                                              2.5    1.2    1.2  1.0  1.1  1.4                                  dissolved in 93 parts                                                         Glycerine                                                                     Glycerine                                                                     Cholic Acid                                   0.2                             PEG 6000           3.0    1.5                                                 Beta Alanine                                                                              1.5                     1.0  0.6                                  Butylcarbitol                                 0.8                             Di-n-butyl-Phthalate                     0.4                                  ______________________________________                                        Example No.     129    130                                                    ______________________________________                                        % Metal         90.0   90.0                                                   Petrolatum A    9.7    10.0                                                   Triethanolamine 3.8    3.7                                                    Glycerine              0.2                                                    Cholic Acid     0.3    0.1                                                    Butylcarbitol   1.2                                                           ______________________________________                                        Alloy Powder: 97.5 Pb/1 Sn/1.5 Ag                                             Example No.    131                                                            ______________________________________                                        % Metal Powder 85.0                                                           Petrolatum A   6.0                                                            Carbowax 3350* .6                                                             Tetraethylene glycol                                                                         0.0                                                            Butyl Carbitol**                                                                             1.92                                                           Triethanolamine                                                                              3.75                                                           7 parts NaOH dissolved in                                                                    0.0                                                            93 parts glycerine                                                            Surfynol 104E***                                                                             0.0                                                            Floral A****   2.73                                                           ______________________________________                                         *Poly(oxy-1,2-ethandiyl),alpha-hydro-omega-hydroxy. (Reg. No.: 2532268-3)     **2(butoxyethoxy)ethanol. (Reg. No.: 11234-5).                                ***2,4,7,9tetramethyl-5-decene-4,7-diol. (Reg. No.: 12686-3).                 ****Floral AK = hydrogenated wood rosin.                                 

Accordingly, it should be evident that one skilled in the art offormulating soft solder metal powder-bearing pastes now has a way for:controlling hot slump to a user's desired specification by formulatingfor diminishing such slump modestly or even clear down to practicallyzero; and for imparting, where necessary or desired, restriction of flowof the molten metal anywhere from a modest desired proportion down toinsignificance. The combination in the instant vehicle ofhydrocarbon/antislump agent-flux system as defined herein provides suchcontrol. Examples 108, 125 and 131 represent "best modes" of carryingout this invention, each being commercial embodiments of the presentinvention.

What is claimed is:
 1. A nonaqueous noncorrosive inorganic salt freepowdered metal soft solder paste composition containing from 75% to 95%by weight of a powdered soft solder metal or powdered soft solder metalalloy having an average particle size finer than 100 mesh (U.S. StandardSieve Size) and .Iadd.a vehicle containing .Iaddend.from .[.5% to 25.]..Iadd.0.5% to 75% .Iaddend.by weight .Iadd.of said vehicle .Iaddend.of anonaqueous organic liquid having a surface tension of from 43 to 65 ormore dynes/cm. at 20° C., and a noncorrosive anhydrous flux.
 2. Animproved essentially nonaqueous noncorrosive inorganic saltfree pastevehicle for soft solder metal powder, said vehicle comprising petrolatumin which is dispersed in a proportion effective for diminishing hotslump of said metal powder when it is compounded with said vehicle, anonaqueous organic liquid, having a surface tension of from 43 to 65 orhigher dynes/cm. at 20° C., and a noncorrosive anhydrous flux.
 3. Animproved essentially nonaqueous noncorrosive inorganic salt free pastevehicle for soft solder metal powder, said vehicle comprising petrolatumin which is dispersed in a proportion effective for diminishing hotslump of said metal powder when it is compounded with said vehicle, abase dispersed in a liquid polyol said polyol having a surface tensionof from 43 to 65 or higher dynes/cm. at 20° C., and a noncorrosiveanhydrous flux.
 4. A nonaqueous noncorrosive inorganic salt freepowdered soft solder metal paste composition in accordance with claim 1wherein the nonaqueous organic liquid is triethanolamine.
 5. Annonaqueous noncorrosive inorganic salt free powdered soft solder metalpaste composition in accordance with claim 1 wherein the nonaqueousorganic liquid is diethanolamine.
 6. The vehicle of claim 3 in whichsaid base is an amino alcohol in a proportion between about 2% and about40%.
 7. The vehicle of claim 6 in which said base is an amino alkane ina proportion between about 2% and about 40%.
 8. The vehicle of claim 3in which the base is sodium hydroxide in a proportion between about0.05% and about 5%.
 9. The paste of claim 1 comprising from about 79-95parts of powdered tin-containing solder which melts below 330° C. andhas a particle size not substantially larger than about 100 mesh. 10.The vehicle of claim 1 which consists essentially of petrolatum, an baseand a polyol having a surface tension of from 43 to 65 or more dynes/cm.at 20° C. and is further characterized by the presence therein of asurfactant.
 11. The vehicle of claim 1 which consists essentially ofpetrolatum, an alkali metal hydroxide and a polyol having a surfacetension of from 43 to 65 or more dynes/cm. at 20° C. and is furthercharacterized by the presence therein of plasticizer or diluent.
 12. Thevehicle of claim 11 wherein at least a portion of said diluent ispractically water insoluble.
 13. The vehicle of claim 12 wherein saiddiluent comprises a phthalate ester.
 14. The vehicle of claim 13 whereinsaid ester is dibutyl phthalate.
 15. The vehicle of claim 11 whereinsaid diluent comprises a terpene alcohol.
 16. The vehicle of claim 3compounded for use with soft solder powder wherein said base is an amineand the vehicle also contains carboxylic acid.
 17. The vehicle of claim16 wherein said carboxylic acid is polycyclic.
 18. The vehicle of claim17 wherein said carboxylic acid is cholic acid.
 19. The vehicle of claim17 wherein said carboxylic acid is a rosin acid.
 20. The vehicle ofclaim 19 wherein said rosin acid is principally abietic acid.
 21. Thevehicle of claim 20 wherein said amine comprises a water solublealkanolamine.
 22. The vehicle of claim 21 wherein said alkanolamine istriethanolamine.
 23. The vehicle of claim 16 wherein said alkalicomprises triethanolamine, said carboxylic acid is cholic acid, and thevehicle is further characterized by the presence of surfactant anddi-n-butyl phthalate diluent.
 24. The vehicle of claim 2 wherein saidliquid polyol comprises glycerine.
 25. A nonaqueous noncorrosiveinorganic salt free soft solder paste characterized by resistance toslumping during heating to the solder fusion point comprising:(a) from75 to 95 weight parts per 100 parts of paste composition of a softsolder metal powder composition having a particle size of from -200 to+400 mesh (U.S. Standard Screen), (b) from 25 to 5 weight parts heatliquefiable hydrocarbon ranging from semi-solid at room temperature tofugitive from the metal powder at the fusion temperature thereof, (c) anonaqueous organic liquid having a surface tension of from 44 to 65dynes/cm. at 20° C. dispersed in said hydrocarbon, and, (d) an amount ofa noncorrosive flux for said soft solder sufficient to form a shiny andcoherent residue of solder upon melting and solifying said powdered softsolder.
 26. A nonaqueous noncorrosive inorganic salt free soft solderpaste as defined in claim 25 wherein the flux is a basic reacting flux.27. A nonaqueous noncorrosive inorganic salt free soft solder paste asdefined in claim 26 wherein the basic reacting flux ia an amine.
 28. Anonaqueous noncorrosive inorganic salt free soft solder paste as definedin claim 27 wherein the amine is a trialkylamine in which the alkylgroup is selected from the same or different alkyl groups containingfrom 2 to 6 carbon atoms.
 29. A nonaqueous noncorrosive inorganic saltfree soft solder paste as defined in claim 28 in which the trialkylamineis triethylamine.
 30. A nonaqueous noncorrosive inorganic salt free softsolder paste as defined in claim 25 in which the flux is an alkali metalhydroxide or an alkali metal alcoholate.
 31. A nonaqueous noncorrosiveinorganic salt free soft solder paste as defined in claim 30 in whichthe alkali metal hydroxide is dissolved in or reacted with the polyol.32. A nonaqueous noncorrosive inorganic salt free soft solder paste asdefined in claim 30 in which the alkali metal hydroxide is sodiumhydroxide.
 33. A nonaqueous noncorrosive inorganic salt free soft solderpaste as defined in claim 25 in which the nonaqueous organic liquid ispolyhydric alcohol containing only the elements C, H, and O.
 34. Anonaqueous noncorrosive inorganic salt free soft solder paste as definedin claim 33 in which the polyhydric alcohol is glycerine.
 35. Anonaqueous noncorrosive inorganic salt free soft solder paste as definedin claim 34 wherein the flux is an alkali metal hydroxide or alcoholate.36. A nonaqueous noncorrosive inorganic salt free soft solder paste asdefined in claim 25 said paste being further characterized by thepresence therein of from 0.5% to 10% by weight of an alkanolamine.
 37. Anonaqueous noncorrosive inorganic salt free soft solder paste as definedin claim 26 wherein the alkanolamine is triethanolamine.
 38. Thecomposition of claim 30 in which the alkali is sodium hydroxide in aproportion between about 0.05% and about 5%.
 39. The paste of claim 25comprising from about 75-95 par1/2ts of powdered tin-containing solderwhich melts below 330° C. and has particle size not substantially largerthan about 100 mesh.
 40. The paste of claim 31 which consistsessentially of petrolatum and said alkali and is characterized by thepresence therein of surfactant.
 41. The paste of claim 31 which consistsessentially of petrolatum and said alkali and is characterized by thepresence therein of plasticizer or solvent diluent.
 42. The paste ofclaim 41 wherein at least a portion of said diluent is water insoluble.43. The paste of claim 42 wherein said diluent comprises a phthalateester.
 44. The paste of claim 43 wherein said ester is dibutylphthalate.
 45. The paste of claim 41 wherein said diluent comprises aterpene alcohol.
 46. The paste of claim 25 which is furthercharacterized by the presence therein of a carboxylic acid.
 47. Thepaste of claim 46 wherein said carboxylic acid is polycyclic.
 48. Thepaste of claim 46 wherein said carboxylic acid is cholic acid.
 49. Thepaste of claim 46 wherein said carboxylic acid is a resin acid.
 50. Thepaste of claim 46 wherein said resin acid is principally abietic acid.51. The paste of claim 40 which is further characterized by the presenceof alkanolamine.
 52. The paste of claim 51 wherein said alkanolamine istriethanolamine.
 53. The paste of claim 39 wherein said alkali comprisessodium hydroxide and glycerine, said carboxylic acid is cholic acid, andthe vehicle is further characterized by the presence of surfactant anddi-n-butyl phthalate diluent.
 54. The paste of claim 25 wherein saidpolyol is glycerine.
 55. The paste of claim 25 wherein theflux/nonaqueous organic liquid system is 7% sodium hydroxide dissolvedin 93% glycerine.
 56. The paste of claim 51 wherein the alkanolamine ismonoethanolamine.
 57. The paste of claim 25 wherein the hydrocarbon is ahydrogenated polymeric hydrocarbon having a softening point in the rangeof 15° to 130° C.